text:
What are the essential elements of a control tower?
Assuming control towers are essential for large airport operation, what is the minimum needed equipment inside the standard control tower to support airport operation?

What else is in a supermarket that does not support shopping?

So, things like bathrooms, which aren't directly necessary for air traffic control, but are nice to have for the personnel...?

Or water cooler?

@mins Surely a radar range is relevant to flying. And, no, I won't stop calling you Shirley. :)

Military combat controllers can set up fairly busy airfield operations very quickly, using just some radios and a few small other things

The document ICAO Doc 9426, part 3 is about planning a control facility, appendices A and B provide answer elements.

The theoretical bare minimum would be a light gun to give light signals to aircraft. A more generally acceptable minimum is a two-way radio to do radio communications with aircraft.
From there up other systems can be added. The list below gives some examples but is not exhaustive.

A telephone. Always useful when you want to get in contact with other parties on the ground (e.g. air traffic control centre) or other parties with you.
Meteorological instruments can provide current wind and visibility at the runway to the tower controller. This is not directly to support the Air Traffic Control function, but to provide information services to pilots.
Airport lighting control: runway (and taxiway) lights are usually controllable from the tower. These systems can become quite complex on larger airports
A display with a feed from an approach radar. This present the air traffic situation around the airport to the controller. Whilst on larger airports the approach controllers are usually not located in the tower itself, smaller airports often combine tower & approach control. Even when approach controllers are physically located elsewhere, the approach radar assists tower controllers as well in building a clear mental picture of the situation.
An emergency button that makes the fire department jump to life.
Surface radar display. This presents the ground traffic situation to the controller. Often not found on small airports, but essential for efficient operations at busy airports, especially in low visibility.
More radio's. To split tower control who do the runways and ground control who do the taxiing aircraft. Further divisions can be made.
A system that shows which runways are active, which are closed for use by the airport authority (e.g. for maintenance)
Electronic flight strip system. The traditional paper strips are now often replaced by a digital equivalent. These E-strip system usually communicate with the whole flight data processing system, correlating strips to radar tracks.
Gate allocation system. It's always nice to now where those arriving aircraft should be directed once they are of the runway.
Gate video systems showing the situation at the gate. (to bust pilots that say they are ready for engine start / pushback whilst they are still loading cargo :-) )
Departure management system. When you have a complex airport with multiple runways and a maze of taxiways, a DMAN may help to get aircraft airborne at the right time in the right sequence in the right direction.
Arrival management system. With many aircraft arriving from all directions, headed for different terminal / gates it helps to have an AMAN to avoid overloading your Terminal Manoeuvring Area with incoming flights competing to be first.
Integration of the Surface radar, DMAN and Gate Allocation System with the lights control system. The level of integration varies. In the most extreme case pilots just have to follow the taxiways that light up green and stop at red stop bars. This avoids a lot of radio communications and confused pilots who didn't exactly remember a taxi clearing involving a dozen of taxiway letters.


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How to calculate the Glide Ratio from Drag & Lift?
I know that $c_{d}=0.03 + 0.095c_{l}^2$.
What is the glide ratio?

It looks like a school exercice

The glide ratio for a given angle of attack is the ratio of lift to drag. Both of these are proportional to the respective coefficients (with a proportionality constant of $\frac12\rho v^2A$), so the glide ratio is simply $c_{\mathrm L}/c_{\mathrm D}$.
Practically, what you're looking for may be the maximal glide ratio. Finding the global maximum of
$$\frac{c_{\mathrm L}}{c_{\mathrm D}} = \frac{c_{\mathrm L}}{0.03+0.095 c_{\mathrm L}^2} = \frac1{c_{\mathrm D}}\sqrt{\frac{c_{\mathrm D}-0.03}{0.095}}=\sqrt{\frac1{0.095}\frac1{c_{\mathrm D}}-\frac{0.03}{0.095}\Bigl(\frac1{c_{\mathrm D}}\Bigr)^2}$$ should be a simple matter of algebra -- for the last expression you don't even need calculus, just finding the apex of a parabola.

Actually, the optimum is when $0.03 = 0.095c_l^2$, so it is at $c_l = 0.562$.

$C_D = C_{D0} + K \cdot C_L^2$ therefore $C_{D0} = 0.03$ and $K = 0.095$
Maximum lift-to-drag ratio occurs at the condition for minimum drag and at this condition $C_D = 2*C_{D0}$ and $C_L = \sqrt{C_{D0}/K}$.
Therefore $\max(L/D) = C_L/C_D = 0.5 \cdot \sqrt{1/(K \cdot C_{D0})} = 9.4$

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text:
Was I nearly involved in an accident?
This is a while ago but it has been bugging me now and then.
On September 11 2011 (yes exactly 10 years after 9/11!) I was flying Easyjet 3467 from London Stansted Airport (STN) to Copenhagen (CPH). Scheduled departure was 18:40 local time but the flight was heavily delayed (around 4 hours as I recall) due to another bizarre incident.
Anyway, as we were finally sitting in the plane and taxiing, suddenly the pilot announces that he just got info that another airplane had been heading to land just where we were and had only been some 60 seconds away! A lot of passengers seemed to gasp for air and the pilot sounded quite shocked as well. But there was no other explanation added.
Is there a database of such events so I could look up more about what happened?
I found the flight on FlightStats (sign in required) but there were no real info.

I cannot find anything in avherald, which is one of the leading sources for incident reporting: http://avherald.com/h?list=&opt=1&offset=20110911000000%2B4798675c

Runway incursion? not common, but not unheard of. Usually caused by mixup between ground control and the tower.

OK thanks didn't know avherald.com. But yeah can't find it either. Maybe it wasn't so serious after all or it didn't get reported. I will lookup runway incursion. Thx :)

Why on earth would a pilot announce that and panic people? Surely you have misunderstood and he was explaining a delay or something like that?

@JamesRyan: I agree and of course it is a possibility I misunderstood. But as I mentioned, the rest of the passengers gasped for air. Of course it could be he just told a joke and I sort of misunderstood the whole situation. That's why I would have liked to find a written record etc. of it (if it exists) because it has been nagging me over the years

No, you were not nearly involved in an accident.
If the flight crew is ready to go, an Airbus A320 takes about 40-50 seconds from the moment take-off clearance is given until lift-off. As soon as the aircraft is off the runway, the next one can land. On some busy airports, 60 seconds between take-off clearance and the next landing is a daily occurrence.
In 60 seconds, there is a lot that can prevent an accident. For example, ATC could instruct the incoming aircraft to go around should the departing traffic not be ready to take-off. This is quite a normal event which happens every day at busy airports around the world. In such a case, the aircraft ready for take-off would have to wait for the incoming traffic to pass overhead. It sounds like you may have experienced such an event.
Here is a video of something similar happening in Birmingham.
Since it is a 'normal' event, there is no central database that tracks these issues.

Great answer. I wonder why would the pilot announce that then?

@MatthewLock Even if it was an exceptionally unusual occurrence, the pilot's announcement did nothing other than create unnecessary concern among the passengers.

@DavidRicherby That's exactly why he's wondering why the pilot announced it.

@Nit the whole statement "finally ... taxiing ... just where we were" seems fishy. Most airports aircraft don't start taxiing anywhere close to where aircraft land. Seems either a case of bad memory or a pilot making a very bad joke.

If a departing aircraft is not yet off the ground when an arriving aircraft reaches decision height inbound for the same runway, wouldn't the arriving aircraft need to go around?

@jwenting Yeah, especially since Stansted appears to have only one (remaining) runway, the only way I can see that you'd be in a place where another aircraft is about to land is the situation mentioned here in DeltaLima's answer: you're departing from the runway it's about to land on. It doesn't look like you'd ever need to cross the runway coming from the passenger terminal there.

@reirab of course it would. And a smart controller would have either the departure delay until the arrival is on the ground, or have the arrival slow down to give the departure time to clear the runway. I've had such a situation happen once, flying from an untowered field. We entered the runway (C182 I think we were in), other aircraft was on short final, broke off the landing, and stalled trying to turn away from our departure path, crashing. I don't think either pilot had a good night's sleep that day.

@jwenting Yikes. This is why it's useful to announce that you're about to land on a runway or that you're about to enter a runway for departure at an uncontrolled field... and to listen for such announcements from others (and to look out the window before entering a runway.) That seems weird that they would actually stall and crash, though. You shouldn't normally be going that slow on short final. A smart controller wouldn't have the departure delay until the arrival is on the ground if the departure is already on the runway, though. :) That would end very badly.

@reirab not sure what they did, but we circled and saw an aircraft lying in a ditch just outside the field perimeter. Could in theory have been another one, but how many aircraft do you get in trouble in a few minutes time on a GA field? :)

Yes one of the things I've been wondering is why the pilot would announce it. I don't remember for how long we had been taxiing before the announcement was made. I just remember we had left the gate. Since the plane was heavily delayed (due to a passenger from the previous trip who apparently were unable to leave the airplane, so we had to wait hours for an ambulance, apparently from a private health insurance, to get cleared to enter the airfield with a lift. It was on 9/11 which also delayed all of this!), it must have been quite late in the evening that this occurred.

The term you want to look for is not "accident", but "incident".

To figure out whether or not a situation qualifies as an “aircraft accident” we must look to the definitions in Part 830. The NTSB defines an “aircraft accident” to mean “an occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight and all such persons have disembarked, and in which any person suffers death or serious injury, or in which the aircraft receives substantial damage.” The first portion of this definition is especially important to note for maintenance and ramp personnel. The initial threshold for classification as an aircraft accident is that the aircraft is being operated “with the intention of flight.”

Since no injury or damage occurred, the even would be classified as an "incident".

In the US, NASA runs the Aviation Safety Reporting System, a publicly searchable database of accidents and incidents.  The data are mostly about events in the US, although some international incidents are included as well.  The incident you mentioned doesn't appear.
The European equivalent appears to be ECCAIRS.  Unfortunately, access to that database is "restricted to authorized authorities."

Thanks for info - could anyone with ECCAIRS access look it up? Any other suggestion of how I might obtain more info? Maybe I should contact the airport og airliner?

By the way, not sure if I agree about the incident/accident distinction. If what the pilot said was true it would have been an incident. My question specifically asks if I was nearly involved in an accident, i.e. what could have been the outcome of this incident under the right (wrong) circumstances.

There was probably no incident.
It just means your plane was ready to take off and had to wait longer than expected. Whenever a plane is ready to go the controller has to decide whether he can let it go or should wait for an incoming plane. The controller was probably just playing it safe and decided to make your plane wait, so the pilot got a little exasperated, "Sorry folks, got to wait for another plane to land."

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On average, how many overhauls will thrust reversers have in their lifetime?
How many overhauls will a wide body aircraft composite thrust reverser undergo in its life? (not including damage, etc.)

That is an oddly specific question -- care to elaborate on what prompted you to ask? I don't recall any recent crashes or incidents linked to thrust reversers.

@Johnny I recall at least one, although not recently.

The answer varies from aircraft to aircraft. The newer varities such as the A380 go for a overhaul in about 1200-1500 hours, whereas the B777's go once in 1600-2000 hours of service.When an aircraft goes to overhaul, only then the thrust reversers go to overhaul, because they are an important component of the engine of modern day aircrafts. Though we do not know when will an aircraft retire, so it i difficult to come at a concrete result. But, talking about B747, many airlines are retiring them at the age of 40 years. So, 40 years = 350400 hours. 350400/2000 = 175(Approx.) So, for a B747 the answer should be like 175, and this does not necessarily implies to other aircrafts as well.

do you have any source for this data?

Its from Wikipedia's time between overhaul article. Then I know that B747 are retiring at the age of 40. And calculations are from MS windows calculator!


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Can thrust reversers alone steer and stop an airliner?
Is it possible to use ONLY thrust reversers to steer and bring a smaller size commercial jet aircraft, with a minimum amount of fuel onboard, to a complete stop, after touching down on a longer than average length commercial airport runway?

possible duplicate of For large jets, what is the primary means of slowing down after landing?

If you have enough runway, you can stop without the use of any stopping mechanism except drag. Is there a maximum distance you're thinking of?

I was thinking in the distance of 8,000 feet, and at sea level...thanks

Steer: No. Stop: Yes.
Thrust reversers are either in or out. They cannot be engaged proportionally to some control setting in the cockpit. Once they are unlocked, the airflow through them sucks them out completely. The only way to vary their braking effect would be to throttle the engine up or down, and airliner engines react rather sluggishly to control inputs. Their responsiveness will not suffice to steer the aircraft; only rudder inputs (and those only at higher speed), nose wheel steering and differential braking with the wheel brakes are suitable for directional control on the ground.
Their braking effect is biggest at high speed and tapers off as the aircraft decelerates. For the first third of the landing run they will help noticeably in slowing the aircraft, but you will need a long runway when you want to land without wheel brakes. Details depend on landing weight, airfield elevation and wind speed.

From a physics perspective, we can calculate the amount of force needed to slow a plane down within a given distance. The stopping distance equation is:
$$d_f=\frac{v_i^2}{2a}$$
If we assume the plane has 7000 ft to stop with only reverse thrust, and the touchdown speed is 130 knots = 220 ft/s, we can solve for acceleration.All calculations will be approximate
$$7000=\frac{220^2}{2a}$$
$$a=3.5 ft/s^2$$
Using the second law of motion, we can find the force required to decelerate a 120,000 lb airplane at that rate.
$$F=ma$$
$$F=120,000\times3.5=415,000ftlb/s^2=13000lbf$$
This is about 25% of the max forward thrust of a 737-700. The engines have a bypass ratio of over 5:1, so it seems reasonable that the engines should be able to average this amount of reverse thrust force. This estimate also ignores all effects of drag or friction that would also help to stop the aircraft.
For steering, the pilots could use differential thrust. It would be more difficult than using the rudder and nose wheel, but it should be sufficient. A sideways wind component would make it more difficult to steer though.

I'm not a commercial pilot but I've just been researching this for other reasons: to look at brake wear mechanisms.
Thrust reversers are normally supposed to be engaged on Airbus and Boeing commercial jets (that have them) when you are landing. Engaging them just means opening/moving the various flaps that divert the flow.
However due to noise regulations, you normally are not allowed to actively use them: so you put the engines into idle thrust. However this has several advantages:
 - the system is set up to allow a much bigger reverse thrust if you need it in a hurry
 - you also don't have any positive thrust from the idle thrust since you have it reversed (which is not negligible, it varies from 3-6% of total max thrust)
The FAR/JAR landing calculations do not assume any credit for reverse thrusters, so in ideal conditions you shouldn't need them. But if you have a system malfunction or other problem (bad braking, poor flap control, slippery runway, short runway, very heavy plane etc) then they can help you.
I believe most big commercial jet engines that have reverse thrust, can go up to 80%-90% of N1 (fan speed). That's because most work by opening up flaps that only divert the fan air output (which is about 80% of the thrust). These are for the "translating cowl type".
Airbus says that on the A330 with the GE CF6-80E1A2 engine, at 150kts and at 90% N1 you get 16,000 lb/engine reverse thrust (sea level). Which is 22% of max thrust. It drops to 8,000 lbs at 0 kts
The reversers that open after the rear of the engine ("target type") probably go to higher percentages, but I don't know how much. They are often on military planes.
I suspect that because of the strict noise abatement rules now in place at most big airports, reverse thrusters are not much used in standard landings. And braking capacity has improved a lot. So if you cannot use them, then you don't have them in th design: which is why the Airbus 380 only has them on two engines. More for emergencies I'd guess.
If you look at the efficiencies of wheel braking and air drag, the air drag works best at high air speeds: which is good, because this is where kinetic energy is the highest. As you slow down it becomes less effective, but then wheel braking can take over and control the deceleration at slower speeds, and where you might want to maneuver more.
Incidentally, you can see how much idle thrust occurs from Airbus and Boeing planes by looking at the charts they provide for Ground Towing Requirements. They tell you how much pullback is on the tow bar for the number of engines that are at idle. These charts are in the files they provide on the following (Section 5):
Airbus Aircraft Characteristics - Airpot and Maintenance Planning
Boeing Aircraft Characteristics - Airpot and Maintenance Planning


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Which commercial aircraft are capable of computer-only landings, without human assistance?
Currently what models of commercial aircraft are capable of landing and safely stopping the aircraft, without any human assistance, other than inputting instructions to the onboard computers.

None. While a number of aircraft are certified for autoland with automatic rollout until safe taxi speed, and some can have the autopilot control rollout until the aircraft completely stops, no commercial aircraft has autopilot control of various critical parts for landing such as the flaps and the landing gear.

Isn't that typically part of approach and not landing?


text:
What causes a plane's wing tips to leave a small white vapor trail?
What is the source for what looks to be small trails of smoke or condensation sometimes coming from the very tips of a jet aircrafts wing tips?

You mean contrails?

Related: Why are some contrails longer than others? - the answer goes into detail.

See:  http://aviation.stackexchange.com/questions/14327

@cpast: Clearly not. Contrails are behind the engines at altitude, these are behind the wing tips during take-off and landing. I don't remember ever seeing them behind airliner, but they are quite common behind fighters which have lower aspect ratio and thus stronger wingtip vortices.

@JanHudec never seen them on an airliner? there you go: MD80 B757 B777

@Federico: Sure they can appear. But behind airliners they only appear when it's really wet while behind fighters they appear in much wider range of weather.

@JanHudec I did not mean to say that you were wrong, I wanted only to provide a visual reference for something you said you've never seen. (also, it's nice to see that in some cases at least they do not form at the wingtip, but at the "flap-tip")

@cpast *chemtrails :P

@JanHudec if you want to observe them on airliners the best conditions are during approach on wet, humid days.  You can often see them streaming off the wingtips as the planes cross the fence in those conditions.

@JanHudec Wikipedia: "Contrails [...] are long, thin artificial clouds that sometimes form behind aircraft. Their formation is most often triggered by the water vapor in the exhaust of aircraft engines, but can also be triggered by changes in air pressure in wingtip vortices or in the air over the entire wing surface." (My emphasis.)

@Federico Nice videos. Bizarrely, the ad I got on one of them was for CFM. Do people really buy jet engines because they saw an ad on YouTube?

@bjb568 Lol nice... I was wondering whether to plug that one myself but you beat me to it XD

@DavidRicherby I've wondered that when seeing Super Bowl ads for GE Aerospace or Cisco switches. Or, even more interestingly, Lockheed Martin advertising a stealth bomber. I can just imagine the conversation, "Well, I was really on the fence about whether I should buy a stealth bomber, but this Super Bowl ad really sold it for me."

These are wingtip vortices, which also appear in formula one, and this article explains the reason quite nicely (including airplane pictures and going into the difference between them and contrails).
The significant paragraph:

After the formation of the vortex, the pressure inside it decreases significantly as compared to the ambient pressure. This results in a significant drop in dew point (which was already below the ambient temperature before the formation of the vortex) but along with it, there is an even greater drop in the vertex core temperature, which transforms the water vapour into water droplets and hence we are able to see the vortices trail coming out of the rear endplates.

The cause is reduced pressure in the wingtip vortex trailing behind the wing. Reduced pressure causes reduced temperature and if ambient humidity is high enough the result is the  condensation you observe.

True - relative humidity is a big factor. I have seen condensation trails on final approach on a summer morning in the tropics - I should have checked what the reported RH was.

As other answers state, the vapor trail from the edge of the wing (or from other sections of the wing in various configurations) is the most visible effect of the wingtip vortex, a phenomenon in aerodynamics of airfoils.
Succinctly put, along most of the wing, the air passing over the wing and the air passing under it are pretty cleanly separated by the wing, and when reintroduced, while there's significant turbulence (creating "induced drag") there's typically very little rotational quality to it; a sheet of air over the top of the wing meets a sheet of air from the bottom, where it mixes and settles.
However, at the wingtip, there's a stark border between air that isn't being separated by the wing and air that is. The air that passes over the top of the wingtip is typically directed downward as it leaves the wing, similar to the rest of the wing, and at the wingtip this downward force, in addition to the pressure differential at the wingtip itself (the higher pressure under the wing seeks to equalize with the lower pressure above it by moving around the wingtip), induces a rotation in the air column behind the wingtip; clockwise on the left wing, counter-clock on the right:

Spinning air creates a volume of lower pressure in the center of the column, like the eye of a hurricane, and when air conditions are just right, this reduction in pressure in the center of the vortex can cause a contrail as the humidity in the air condenses into fog. The greater the force of lift produced by the wing, the more forceful and thus larger these vortices can be; wingtip vortices behind large commercial airliners can extend for miles behind the airliner, posing problems for smaller craft in their wake especially in airport traffic patterns. Smaller craft, especially fighter jets, can produce similar contrails in high-G maneuvers as the higher angle of attack of the wing produces a severe pressure differential just above the wingtips, increasing the vortex effect. Modern 4.5 and 5th-generation jets with stealth in mind are designed to avoid this as it's a visual cue to the jet's location.
The effect can be even more pronounced at the edges of deployed flaps, closer to the aircraft fuselage; here the flaps are inducing even more of a downward force on the air, and there's a similar discontinuity between the corner of the flap and the relatively straight wing next to it. Flaps are also typically deployed at lower altitudes where the air's thicker, warmer and can hold more moisture, so the atmospheric conditions for producing a vapor trail are more easily met:


text:
Can the wheel brakes hold an airliner in place if its engines are at full thrust?
Are wheel brakes on most commercial jet airliners capable of holding the jet stationary on a dry surface, if all the engines are given full thrust? Could doing this be potentially unsafe or damaging to any of the aircrafts other structures,  such as pylons, wings, etc.

All vehicles usually have at least one braking system that exceeds engine HP, usually by least several times.  Otherwise the braking effect wouldn't be effective and in some cases useless.  This is a general rule that applies to anything that is braked.

Yes they are. In fact this is required for a static takeoff. A static take-off means setting the brakes and running up the engines to takeoff power then when ready they release the brakes and start the takeoff roll.
Besides that one of the test Airliners have to withstand is a worst-case V1 abort.
This means starting a takeoff and at the last second slam the brakes, come to a stop and then taxi around for 5 minutes. This all needs to happen fully-loaded and with worn brakes that are still certified safe to use.
Between hitting the brakes and coming to a stop the engines will not have time to spool down and stop providing takeoff power.
Airliner mechanics also do engine run-up tests essentially powering up the engine and going through the power range and making sure it works as specified. This is usually 1 engine at a time.
In these run-up tests loose debris (including cars) can be thrown around by the engine blast. So it's important to keep the area clear.

Not if its icy though. Wintertime in the emb145 during crossbleed starts or ice tests we would slide.

@casey the question did specify a dry surface.

For your last paragraph it might be good to mention some layman-friendly demonstrations of the power of jet blast, like the Mythbusters "Jet Taxi" experiment, https://www.youtube.com/watch?v=CpX1riSTeJc, and the Jackass 3D jet engine bit, https://www.youtube.com/watch?v=Ui3KoDIhnSA (NSFW for a few bits of language but visually pretty clean unlike most of the rest of the movie). Both bits are good illustrations of both a static engine runup with brakes in place, and the awesome power behind a jet engine.

Note that when holding stationary, the brakes only have to withstand the force of the engine, but they do not dissipate any power. The brakes could hold stationary any duration without wear and without heating up. This is very different from braking at speed.

Mythbusters 'Jet Taxi' link in Keith's comment seems to be dead now, but here's a working one.


text:
Why don't pilots always use autoland?
In aeroplanes that are equipped for autoland and landing at an airport with a working and adequate instrument landing system for the conditions, why would a pilot choose not to use autoland?
If I had to guess, I'd say it's due to some of the following:

Autoland is stressful and labour-intensive for pilots compared with flying the plane normally down to the ground in VMC.
Autoland produces less comfortable or otherwise "worse" quality landings.
Using autoland is less fun or enjoyable for the pilots.
The use of autoland is restricted by aviation regulations.

But I don't have any sources to back up these claims.

Because someday, somewhere, sometime, it won't be available.  And they need to be proficient at hand-flying when autolanding isn't an option.  If they cannot hand-fly, bad things happen

To legally use autoland, that use must be permitted by the operators operation specifications. The two 747 carriers I worked for in the 1990s deliberately left that out of their op specs because (1) it's expensive to maintain, (2) they didn't want to spend the resources to train for it, and (3) they didn't conduct operations down to minimums that would require autoland. Though not maintained, the autoland systems were typically (but not always) still hooked up, and we would occasionally do one for fun (even though it was technically illegal). They produced really crappy landings back then.

There are a number of reasons why pilot don't use autoland all the time, even if the airport and aircraft are equipped with the right equipment.
To name the two most important ones:

Pilots need to practise their flying technique. If they would always
fly autopilot, they would lose the skills to fly. Skills that they
need when the autopilot does fail. There are phases of flight where
it is better or even required to let the autopilot do its job, but
landing is one the things pilot are allowed to and need to be capable
of doing themselves. Of course autoland needs to be practised as well.
Auto land requires very accurate ILS guidance. Even if the airport is
equipped with calibrated ILS Cat IIIb equipment (required for
autoland), the signals will be degraded by traffic that is operating
near the ILS antennas. Under low visibility circumstances, when
pilots cannot land visually, traffic spacing is increased and ground
vehicles are not allowed anywhere near the ILS antennas to ensure the
best possible signal quality. This is a standard part of the Low
Visibility Procedures (LVP) of all airports. The downside of this is
that the capacity of the airport is reduced. If autoland would be
performed while there is no ILS signal protection, the effects can be
spectacular at best or fatal at worst.

Photo by BFU, incident report here

To be honest all these reasons sound like technical problems that can be overcome. Practicing flying technique could be done once a week to keep from being rusty. A high quality front camera combined with modern image processing could replace the reliance on ILS (the pilot has to use vision, after all). And as for "rough" landings, that just sounds like a property of old fashioned autoland systems. Surely they could be tuned to provide a smoother landing than the average human pilot?

@Jez I am sure the technical problems can be overcome, but the business case has to be positive as well. To justify the enormous investment required, you need to save the money somewhere. Where are the benefits?

Autoland is typically only used when it absolute has to, which means when the weather dictates or when it needs to be used for currency requirements.  ATC doesn't care if you are going to do one, but I have heard guys give courtesy calls to the tower letting them know they'd be autolanding.
The biggest pain with autoland is that it is a monitored approach.  My only experience with those are in Category II ILS approaches (though my aircraft did not have autoland capability).  Monitored approaches are higher workload and are briefed and flown differently than normal approaches*.  As noted by another answer, when you are going to fly an ILS to cat II or III minimums, the ground controllers need to be protecting the ILS critical areas to guarantee the glideslope quality if you are going to follow it below cat I minimums.  This may require coordination with the tower controller.
Lastly, other pilots I've asked about autolands in Boeing widebody aircraft have all told me some variation of not liking to autoland unless they have to do one per company procedures.
*Feel free to follow "What is a monitored approach?" in another question and read more about specific question.

"ATC doesn't care if you are going to do one" and "the ground controllers need to be protecting the ILS critical areas" seems to be contradicting statements, could you elaborate?

ATC doesn't care (they won't stop you) but they do need to be aware that you are doing it if and only if you are using it below Cat I minimums (ie they need to know if you are using it "properly" due to poor visibility, or just doing it for practice in good visibility and could take over if there's a problem below Cat I minimum). It's good etiquette to inform them anyway, but it's not required.

Sorry i didnt see it earlier. I add link to your new question already

Good answer! Just  want to mention that not all autolands must be a monitored approach.It’s probably just a company procedure, or recommended sop on your type. I know both Boeing and Airbus companies perfoming normal automatic approaches and autolands in EASA-land

There is a percieved public belief that autolands are safer (and better?) than manual landings, neither of which I believe to be true.
‘Better’ is a subjective quality, though I certainly pride myself to achieve smoother touchdowns than an autoland, the reality is an autoland is always rougher and more violent than the worst manual landing by any rookie pilot. In fact, it’s quite an insider joke to tell the cabin crew it was an autoland and blame it on the machine whenever I have a bad manual landing.The word ‘positive landing’ was on the engineer’s minds.
‘Safer’ , now that is the real point: autolands are a necessary evil, which we put up with in bad weather because we would not be able to land manually/visually otherwise. I would argue the chance of the machine cocking up the approach is higher than a well-train pilot not being able to land manually. People screwup or become incapacitated aswell, but the chance to manually save the aircraft from a malfunctioning autopilot at 50’ durring autolanding are slim at best:
On my a/c the PM needs to call ‘Flare’ or ‘No Flare’ at 30 feet , indicating to the other pilot that the machine is working correctly or not, in which case the PF must take manual action to save the day. This in zero visibility, below 30’ (hopefully above the runway), in an aircraft flying 140kts and descending at +700 feet per minute. And you ask why we don’t do that every day?
TLDR: Autolands are not better nor safer than a well-trained pilot’s manual landing. They are used when necssary, as a secondary option

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How would you brief passengers who will try flying your plane?
Following up on this question about pilots letting passengers fly the plane, suppose you’re in a Cessna 172 with passengers and you have your PPL. If you want to let a friend try flying the plane, you might climb to 3,000' AGL and get clear of other traffic. You’d probably get to $V_A$ or a little less and trim for level flight. Then, you might let them try some shallow turns. You’d probably say:

Don’t fight me on the controls
If I say let go, let go immediately
Don’t move any of the controls very rapidly
Don’t move any of the controls to their limits

What else might you say? Are these things correct? What else might you let them try?

Rule #1: Don't hit anything. Rule #2: Don't do nuthin' dumb. ;)

When this first happened to me, the pilot first instructed me to clearly say "I have control", "You have control" etc when passing control back and forth. He didn't stick to this rule himself which I found disconcerting :-)

@RedGrittyBrick Yeah, I've never once had an instructor correctly follow the AIM-recommended "positive transfer of control" procedure. Even the ones who pre-brief me on it.

Push forward the houses get bigger. Pull back, the houses get smaller. Keep pulling back and the houses get bigger again.

Ask Otto, he has a lot of good advice.  :-)

@Magnetoz Do nothing at all and eventually the houses get bigger again.

Some version of this MAY work. Discussing real risks MAY help. || I used to be somewhat aware of the risks when flying commercially. Not "scared" but always wary. When planning a flight across the diagonal of China (destination Urumqi) i looked through airline aitrcraft loss records to see if any airline was better or worse fatality wise. All were similar and most had lost one aircraft more than 10 years ago and none in the last 10 years. ...

... Without my intention or immediate awareness this completely removed my "risk awareness" to the point that I had to force myself to listen to standard safety briefings "just in case" as I travelled moderately often.

I find that virtually all the passengers I've let fly for the first time were already so scared of the controls that no "safety briefing" of that sort was necessary.

Don't fight me on the controls.
If I say let go, let go immediately.

If you suspect there's even a remote chance of either of these problems, maybe you shouldn't be letting this person fly your plane.

Don't move any of the controls very rapidly.
Don't move any of the controls to their limits.

In most small airplanes without hydraulics, it takes quite a bit of force to deflect any of the controls rapidly to their limits. And as soon as your first-time passenger starts to push on the controls, they're going to feel increasingly strong g-forces as the plane responds. For first-timers, this is usually a pretty intimidating feel. If someone is pushing too hard, they're going to feel it, and almost certainly back off or let go entirely.

"Positive transfer of control" using 3-step acknowledgment such as "You have the controls" / "I have the controls" / "You have the controls" is a good idea for flight training, or for flights with 2 pilots taking turns at the controls; but in my opinion it's not necessary for a joyride with a friend. As the PIC, and the only licensed pilot in the cockpit, you need to be monitoring the situation at all times anyway. If you decide the situation requires you to reassert control, you can simply ask them to release the controls. If you can't trust the person to do this promptly, you probably shouldn't be letting them fly your plane anyway; a preflight safety briefing isn't going to solve that.

To be as safe as possible, you can take the following steps before allowing your passenger to fly (some of these you already stated):

Select a location away from controlled airspace, busy airway/routes, or other special-use areas like drop zones.
(Optionally, if you don't mind the extra radio chatter) Tune a nearby ATC radar facility (approach/center) and request radar advisories. Tell them you'll be maneuvering in a certain area.
Climb to a sufficient altitude to allow good clearance from all terrain and obstacles (antennas, etc.), and to allow enough altitude for recovery if your passenger should somehow manage to stall or enter a steep dive or something.
Trim for straight & level flight at $V_A$ for your current weight (lower than the gross-weight $V_A$ you get out of the book).
Make a set of clearing turns and scan for any traffic in the area.
Give your systems a once-over and verify you have sufficient fuel.
Hand over the controls!

You didn't specifically ask about this, but I've flown with a lot of first-time passengers, people who have never been in an airplane. Both children and adults. Many of them are understandably quite nervous. Here are some things I try to do to make it as easy, fun, relaxed and stress-free as possible for them:

Give them a simplified, plain English description of the flight. Tell them exactly what you plan to do and what order things will happen in. E.g.

First we're going to start the engine. I'll get on the radio and get clearance from the control tower. Then we'll taxi out to the runway and stop for a few minutes while I go through some checks to make sure the plane's in good shape. Then we'll take off and head out to the east to do some sightseeing. While we're up there, if you're comfortable and would like to try your hand at the controls, we can do that. When we're done with that we'll turn around and head back to the airport, land, and taxi back in.

Don't use fancy words or terms that a non-pilot wouldn't understand.
Help them enter the airplane. Show them how to open and shut the door. Show them how to buckle and unbuckle their seat belt.
Ask them if they have any questions.
Do your normal preflight safety briefing, again using simplified English and avoiding pilot terms. Limit it to points that are relevant to a passenger (avoiding the controls, staying quiet if asked, opening the door). They do NOT need to hear about what you're going to do if you have an engine failure on climbout. If this is a normal part of your preflight / before takeoff briefing (as it should be), say it to yourself mentally, not out loud.

During the flight:

Talk your way through everything you're doing. When you're ready to do your run-up, tell them:

I'm about to run the engine up to power to make sure everything's running smoothly. I'm holding the brakes so we're not going to go anywhere, but the engine will get pretty loud for a minute.

When you're doing your magneto / prop governor checks:

Now I'm going to do some things to the engine to make sure it's running right. It's going to make some pretty funny noises, but it's perfectly normal.

Talking through everything accomplishes a few goals:

Avoids startling the passenger with something unexpected. A prop governor check sounds really bad to somebody who knows about engines but nothing about planes. A stall horn in the flare may be perfectly normal to you but a loud buzzing alarm is the last thing the first-timer will be expecting to hear. Tell them about it ahead of time.
Makes the passenger feel like they're a part of the flight and not just dead weight in the plane.
Keeps you focused on your tasks as PIC and discourages you from getting distracted in conversation with your passenger.

Make the flight as smooth as possible. Don't overcontrol the airplane. If you drift 100' from your intended altitude, don't pull 2 g's to get back up to it. Make it slow and gentle. They're not a pilot, chances are they're not going to know you drifted 100 feet. They will know if you jerk the thing around. DO NOT hot dog the airplane. You may be bored with slow, gentle flight, but your passenger isn't.
Speak slowly, clearly and confidently.
Smile and try to look like you're having fun. Your first-time passenger is probably feeling pretty vulnerable. When people are vulnerable they feed on the emotions of the people around them. If you look like you're having the time of your life, they're probably going to have fun too. If you look angry, ticked off or scared, you're going to scare them too even if the flight is perfectly smooth. This is especially true and critically important with children!

If/when they're ready to take the controls:

Show them how the yoke controls pitch and roll. Do some (very) gentle climbs and rolls to illustrate what various control inputs do.
Tell them to look outside and not to worry about all the fancy intimidating lights and dials in the cockpit. Tell them that the only tool a pilot needs to fly the plane in good weather is their eyes.
Tell them to relax and have fun! Assure them that they aren't going to crash the plane or break anything and that you're there watching and won't let them do anything unsafe.
After a few minutes, once they get the hang of basic control inputs, you can start to tell them about sight references: show them how to look at the horizon and tell if they're banked, climbing or descending. After 15-30 minutes you should be able to get virtually any passenger to be able to hold straight & level attitude and make gentle turns. Being able to accomplish this is very rewarding for your passenger and makes them feel like they achieved something. It encourages their excitement about aviation and makes them want to fly again.
Don't forget to do your job: scan for traffic. Monitor your engine gauges. Listen for ATC calls. Don't stray into controlled airspace. "Maintain situational awareness."

I've had a great deal of success using these tips when flying with first-timers and children. In 16 years of flying I have had only one bad experience, with an adult passenger who had an unknown (to me) and pretty severe anxiety problem and had a panic attack shortly after takeoff. A couple of kids have fallen asleep on me (which I took as a compliment). Everyone else had the time of their life. And let me tell you... if you're someone who loves flying, there is no better feeling than sharing that with someone else and watching their excitement. It's the closest you'll ever come to reliving your own first flight, which hopefully you remember fondly because somebody cared as much as you do about being the best possible ambassador for aviation!

And if they freeze up and won't let go.. just cover their eyes they will quickly let go to try and remove your hands. (Although that's extremely rare) I usually also tell them that if I help them a little bit or something don't let go, but if I say I have the flight controls then let go. Because some people will drop everything the minute you reach for yoke even if what just putting your hand up as a precaution. That happens much more often (but less if you tell them to keep flying even you assist them a little without asking for the controls back). Great write up BTW.

excellent and detailed answer, thanks!

just my two cents, as what not to do, on my first flight, the pilot said pretty much nothing to us during the whole flight. I already loved aviation before that flight, so I didn't mind too much, as I knew what to look for and what to expect. But it does make you feel uncomfortable to have a cold wall between you and the pilot. ;)

Besides the points you mentioned, on my introductory flight my instructor was very clear regarding shifting the commands from one person to the other on the plane.
When handing over commands he told me to specify clearly with the words
Handing Over Commands
whenever I would feel uncomfortable or he would feel that he had to take back control. This was done to clearly mark who was handling the aircraft in order to avoid confusion and get into a situation where dangerous things could happen.


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Is the altimeter setting corrected for temperature?
In an ATIS or AWOS/ASOS recording, is the reported altimeter setting corrected for temperature?
I think it must be, because on a hot day, the altimeter should still show correct field elevation. If it wasn’t corrected for temperature, then the reported field elevation could be badly wrong on a really hot or really cold day.
(This and other questions describe pressure and density more generally.)

The reported altimeter setting, QNH, is 'somewhat' corrected for temperature, in that it corrects for temperature error at the aerodrome elevation. This is the main difference between the more-meteorologicaly-inclined QFF which does not contain this temperature correction.
You will still get altimeter errors because of the high/low temperature while being above (or below) the aerodrome  (about 40 ft for each 1000ft for each 10 degrees C), but the actual temperature error at aerodrome level will be 0.

The given sea level pressure from an ATIS will reflect the local deviation from standard temperature such that your altimeter (which does not correct for temperature) displays field elevation on the ground.
It is important to note that the ATIS/AWOS/ASOS station is directly sampling station pressure, not sea level pressure, which must be derived.  The equation used to do this is the hypsometric equation and there is an assumption of temperature in the atmospheric layer between the ground and sea level.
$$(z_2 - z_1) = \dfrac{R\cdot\bar{T}}{g}\ln\left(\dfrac{p_1}{p_2}\right)$$
In this equation $z_1$ is 0 m, $z_2$ is station elevation, $R$ is the gas constant for dry air, $\bar{T}$ is the average temperature between $z_1$ and $z_2$, $p_1$ is sea level pressure (hPa), $p_2$ is station pressure (hPa) and $g$ is acceleration due to gravity.  All are known except $p_1$ (assumptions about $\bar{T}$ are made from the lapse rate of the standard atmosphere and station temperature). Solving for $p_1$ yeilds:
$$p_1 = p_2 \exp \left( \dfrac{g z_2}{R \bar{T}} \right)$$

The altimeter is adjusted for air pressure, which is a function of temperature (and altitude). So the answer to your question is yes.
That is why it is bad for an airport to be "hot and high" (think Phoenix in the summer), the high altitude is compounded with nearly 100°F (40C) temps, makes for very thin air.


text:
How does a CVR / FDR determine when to stop recording?
For example, the CVR records only about 2 hours of data.
Overwriting important data must be avoided, and thus the recorders should know if a catastrophe has happened. Then they can stop recording (to protect the already recorded data from overwriting), and start signaling the rescue team.
What is the logic used to stop recording?

The CVR and FDR have impact switches to stop recording when they experience high acceleration. In incidents and accidents that don't involve high enough acceleration, the plane remains intact enough for the boxes to be immediately found and switched off manually. In more serious crashes, the boxes stop recording because of the physical destruction of everything but the memory units (only the memory units are built to survive crashes).

I had guessed: when the power cables to the unit have been ripped off. Is this a valid case?

@aitchnyu: Yes; in many crashes, the flight recorders' chasses (which are armoured, cushioned, insulated, the whole nine cubic yards, though not quite as much as the memory modules themselves) survive completely intact, instead of just the memory modules, but the power cables (which are completely crash-unprotected) do not.

In the United States, CVRs and FDRs have a 10 minute (+/- 1 minute) battery requirement to allow any available post-crash voice and data to be recorded, with power removed once a timer limit is reached.
While I'm not familiar with the internals of the FDR, simple circuitry could trigger the timer to start based on current flow from the battery, if not for an acceleration-based impact sensor suggested.

The wording of the linked rule seems to suggest that the independent-power-source requirement is more intended to allow the flight recorders to continue operating if the aircraft suffers an electrical failure in flight, rather than to ensure post-crash operation.

...if not for the rule in (d)(2) to remove that power after 10 minutes as well.

If it were meant to ensure post-crash operation, there wouldn't be any point in including a requirement to also power the cockpit area microphone for that length of time, given that the CAM won't be functioning after a crash anyways.

In crash the last two hours before the crash is most important, so the recorder always recording and stopping when the plane crashes either because of crash sensor or simply due to loss of power and input as the wires leading to it are torn by the impact forces is the right thing.
However in some incidents¹ the data would also be useful. When the crew realizes something occurred that needs to be reported as incident, they are supposed to pull the circuit breakers after landing and tell the appropriate safety board to come for the data (which must be done before next flight). Alternatively if the aircraft is equipped with quick access recorder² they can instead preserve those data, which can be done by any maintenance worker, so the plane can be dispatched again.
However sometimes the crew fails to realize they should preserve the data (or fail to report the incident altogether and it may be reported by someone else like another crew, traffic controller, maintenance etc.) and get scolded for it.

¹ Incident is any occurrence in which safety margins were reduced, but nobody was hurt and there was no or only small damage (with damage to engines or landing gear always considered small). The kind of incident where investigators would most want to have CVR and FDR data and don't always get them is TCAS activations (near misses); they generally have ATC voice recordings and radar tracks, which ATC records in much longer loop, but the on-board recorders often get overwritten either before the planes land or because the crews fail to preserve them.
² The quick access recorder is not crash-worthy and not mandatory, but most airliners have it these days. It usually has longer recording loop and records more parameters, but the main advantage is that any mechanic with portable computer can download the data in couple of minutes and the aircraft can be dispatched again instead of waiting for the safety board investigator to come around.

"the last two hours before the crash is most important" - Almost always, but probably not in the case of MH370.

@RedGrittyBrick: I wonder why the new types don't store longer recording. Quick calculation tells me the raw 4-channel sound would be around 1¼Gb/h which does not sound like that much (yes, it should probably not use the most integrated chips as resilience is more important, and it is probably stored in multiple copies but I would still expect a bit more to fit in the box).

Agreed. Maybe the businesses involved just don't voluntarily make improvements over what regulations require (set in the days of magnetic tape recording). I don't understand what significant obstacles there could be other than institutional inertia and maybe certification costs.

What if there's a TCAS activation, so they stop the recorders, and then later in the flight they crash?

@raptortech97: They don't. They should do it after landing. So if it's more than 2 hours, the recording won't be there anyway (it may be in the QAR though, they usually have more data).

@JanHudec oh, thanks! That makes sense. And the FDR will probably still have the data, which is something at least.

@JanHudec: I know of at least one case (a near-MAC in the 60s or 70s; I'll add a link when I get home and can look it up) where the flightcrew of one of the planes involved pulled the CVR's breaker a few minutes after the fact, which significantly aided the NTSB's investigation; OTOH, this was back when they only recorded 30 minutes (usually plus one or two more to be on the safe side), rather than 120, so preserving the recording would have been significantly more time-critical than it would nowadays.


text:
What is the history of the aircraft logbook?
I need to know when the mandate to maintain a logbook started. Was it a US requirement, or was it from another regulator in the world? Did the aircraft logbook start at the same time as the pilot logbook?

Well I'm pretty sure the Wright Brothers had some sort of am aircraft logbook... But no idea on the regulations side

Similar to several other terms (e.g. port and starboard), the logging formats came from the shipping industry. Ship used to have detailed logs about their voyages.
Smithsonian states in an article:

In a logbook from 1913, a pilot penned on one page the date of a
flight, airplane used, passenger’s name, time aloft, and course flown.
On the opposite page, he recorded height achieved, distance, weather,
and remarks.

The above-mentioned article also tells:

The Wright brothers kept detailed notebooks, recording dispassionately
the results of their experiments in building the first airplane.

In the US, pilots are required to document their flights in logbooks if they want to use the hours toward certification requirements. (14 CFR 61.51). The only time when one should not log time is if the flight time would normally be considered illegal compensation; in such cases, the pilot can make the flight legal by not logging the time, but these unlogged hours will not be counted toward requirements for certificates.


text:
What do jet pilots say during the takeoff as they are speeding down the runway?
I was watching a documentary on youtube and the pilots always say something that sounds like "B1E" when they have enough speed to take off. What exactly are they saying, and why do they say it?

Weeeeeeeee........

Certainly it could be a better technical term.

@dotancohen: only for graduates of civilian "how to fly a aero-plane" schools. For ex-Air Force types I believe the proper thing to do is sing a chorus of "Off we go into the wild blue yonder". Navy types should warble a raucous chorus of "Anchors Aweigh!" during take-off roll, former Marine Corps fliers can either sing the Marine Corps Hymn or shout "Hoo-raw!" repeatedly, and ex-Army chopper pilots just sit and wonder why they're not hearing "whopitta-whopitta-whop" as they go rolling along.

@dotancohen I was going for "Our Father who art in Heaven..."  :-) but yours is the winner!

What you are hearing is "V-One", written as V1.
It actually is said when they can no longer safely abort the takeoff with the remaining runway, but they still are not quite ready to takeoff.
As they get a little faster, there should then be a second callout of "Rotate" when they have achieved the required takeoff speed, and that is when they actually takeoff.
To answer the "why" part, it is said by the pilot who isn't actually flying the airplane since he has more time to monitor the speed and can say it at exactly the right time.  It alerts the other pilot that it is no longer safe to abort the takeoff and that pretty much no matter what happens now, they should continue and come back to land if needed.
Edit:
In my answer above, I simplified somewhat by only mentioning the available runway.  There are other factors that can come into play even with a runway that is longer than needed.  One example would be the speed after which the brakes can no longer stop the airplane because they would over-heat and become ineffective.  This is known as the brake energy limit, and it is not safe to abort above this speed, even if you have "plenty" of runway.
V1 must be calculated or looked up prior to every takeoff, along with the other performance numbers.  They vary based on the weight of the aircraft, the configuration of the aircraft, the altitude of the runway, and the weather (outside temperature, wind, etc.).  Sometimes this is done via a computer and sometimes manually via lookup tables or even graphs.
For an example of the graphs, and more information about how temperature and altitude affect takeoff performance, see my previous answer here:
Does temperature affect takeoff performance?
There are also times when a pilot may increase or decrease V1 intentionally, even when it is not required.  For instance, if there is wet ice on the runway it may not be safe to abort even at a very low speed, so you would be forced to continue no matter what (note that I'm NOT saying that this is a good idea). Using a lower power setting to extend engine life is another example, and you can read about it in my question here:
Why would an airplane pilot choose to intentionally use more runway than required for a takeoff?
For way more information than you probably care about takeoff performance, see my other answer here:
Minimum Runway Length and V1
In closing, aircraft performance planning is a rather complicated subject and it is only one of many subjects that we must master in order to safely fly an airplane.  This only just scratches the surface of it, and there is a lot more that must be considered (such as "hey, will we be able to out-climb that tree off the end of the runway?").

Departure in BIRK as a good example.

From the 1990s at two different airlines in 747-100 and -200 aircraft with 3-man crews. Call outs were the same regardless of whether it was the the Captain or the F.O. flying, so PF=Pilot Flying, NFP=Non Flying Pilot, and FE-Flight Engineer.
We'll assume a standard takeoff with more than adequate runway length, no runway contamination. The airplane is lined up, flaps at 10 degrees, the PF is on the brakes. The FE has rotated his seat to a position between the pilots and as far forward as possible. The PF has his hand on the top of the thrust levers. The FE has his hands positioned so that he can readily reach the bottom of the thrust levers to retard them should the PF overboost. Both pilots are primarily looking out the front windshield. The FE is watching the fuel flows, EPRs, and EGTs on the front panel.
When takeoff clearance is given, the PF starts advancing the thrust levers. The first call comes when it's obvious that all engines are powering up:
PF: "set takeoff power" The call is to the FE, but the PF keeps his hands lightly on the thrust levers in case of an abort. The FE moves the thrust levers to the desired power setting using the EPRs. He may need to jockey them a little.
FE: "power set" given when the FE is happy with the setting, although he will continue to monitor and adjust as necessary.
NFP: "80 knots" Used by only one of the airlines I flew for. They had an ops specs requirement that if you didn't have full direction control at 80 knots, you were to abort the takeoff. It was in my opinion an unneeded call, and that call plus the actions of a captain very much concerned with following the rules resulted in putting an airplane off a runway at KJFK. The airplane was totaled, only minor injuries.
NFP: "V1" The PF takes his hands off the thrust levers since an abort is no longer an option.
NFP: "rotate" The PF starts raising the nose to a pre-determined pitch attitude, more often than not 12 or 13 degrees.
NFP: "positive rate" Given by the NFP when he observes the vertical speed go positive. There were also operational noises caused by the removal of the locks that kept the gear lever from being positioned to UP when the aircraft was on the ground.
PF: "gear up" The NFP positions the gear lever to the UP position.
NFP: "V2" Given when the airplane has accelerated to that speed. The PF will maintain that speed until a clean-up height, typically 1000 -1500 feet AGL.
NFP: "transition" The PF lower the nose to around 5 degrees to start accelerating.
PF: "climb power" The FE brings the thrust levers back to climb power.
FE: "power set"
PF: "flaps 5" Given when the aircraft has accelerated to the minimum safe airspeed for that configuration. The NFP sets the flaps
PF: "flaps 1" Again, given when the aircraft has accelerated. At flaps 1 the trailing edge flaps are up, but the leading edge devices are still out.
PF: "flaps up" This gives you a clean wing.
Bear in mind that the speeds vary with runway altitude, ambient temperature, and weight of the aircraft. Back in the dark ages of the 1990s these speeds were grease-penciled in on a plastic card by the FE. The card was then handed to the F.O. for verification, and then placed at the front of the thrust level console in easy view. Then the two pilots would position 5 plastic bugs around the perimeter of the airspeed indicator to those speeds.
Also bear in mind that this is an 76 year-old man relating from memory that which he last did 16 years ago. He did do it a lot of times, though.

Terry, you keep discounting your answers as the reminiscences of an old man... I'm here to tell you that I find them very informative, practical, and told with the panache of a great story teller. Many here can quote FAA regs in their sleep, but you bring them to life. While our ages would have me call you "Dad", you sound like the kind of guy I'd love to call "Grandpa"!

I wonder how this would vary for a 747-400 or 747-8, which have two-person flight crews?

@Sean Never having flown a transport category aircraft with a two-person crew, I can't say except to note a couple of things. The obvious, of course, is the lack of a flight engineer. The perhaps not so obvious is that computers now pretty much take care of much of what the f.e. did. And I would be very surprised if actual physical plastic bugs are used on the airspeed indicator.

authors: Bob Jarvis - Слава Україні


text:
Is it possible to recover dumped fuel?
During emergencies pilots are authorised to dump fuel, but is there any way or method to recover the fuel that has been jettisoned?

An airline will pay about $256,416 for a full load of fuel on an A380, but an alternative to jettisoning fuel will probably cost much more than that to put on every plane.

@fooot "about $256,416". Are you sure it's not $256,417.32? It's kinda silly to give six significant figures when you've said "about".

@DavidRicherby I realize it seems weird, I debated rounding it but decided it didn't matter much. Each person can decide how many significant figures to throw out based on how much they trust or agree with it.

@DavidRicherby I actually consider giving a too precise value as one means of sarcasm :D

In theory it could be done, you could rapidly dump fuel into empty tanks below the wings and drop them. At a certain height they deploy Parachutes and land. Just like the Space Shuttle ejects the side tanks.
But where?
Some fuel dumps are only authorized over water and it would cost more to rescue the tanks and bring them back to the airline.
Over land they'd probably smash into populated areas.
The cost for saving some thousands of $ of fuel is not fesable for the rescue.
Short answer yeah it could be possible, but dangerous and costly.

Use kevlar tanks, like in F1

In practical terms, no. If you wanted to save/recover the dumped fuel then you would have only two basic options: dump the fuel as usual and then recover it somehow from the air; or, pump the fuel in a controlled way into a container outside the aircraft.
The first option is probably impossible: how could you capture a huge cloud of fuel and fuel vapor mixed with the air? That would be like gathering water from clouds.
The second is theoretically possible, but for civil aviation at least it probably requires too much equipment and risk. You could pump the fuel into a drop tank then jettison it with a parachute for a soft landing. Or you could pump the fuel into another aircraft via a tube, in a kind of reverse air-to-air refuelling. Or if you're dumping fuel from a  helicopter (does that ever happen?) it could hover over a tank on the ground, pump out the fuel and then land.
But all of those suggestions are totally impractical (again, at least for civil aviation). Adding drop tanks or air-to-air hoses would add huge cost in materials and training and reduce the useful load of the aircraft significantly, all for a situation that rarely occurs. And for air-to-air pumping you would need an empty tanker aircraft to be available immediately, which is highly unlikely, plus there is the inherent danger of operating two aircraft very close together.
Since fuel dumping is an exceptional situation and many aircraft can't dump fuel anyway, it seems unlikely that investing in a recovery solution would be worthwhile.

I don't think helicopters need to dump fuel because max landing weight is equal to max takeoff (and you only need to be able to dump fuel if there is a 5% difference)

Not to mention the fact that (unless the landing is required due to a medical emergency), air-to-air refuelling is the last thing you want to do with a stricken aircraft. Oh, and the cost of training all airliner pilots to execute it safely.

I can't see why a helicopter would ever need to dump fuel for weight reasons - if you can hover above the tank, you can just hover above the landing zone, and then hover slightly lower....until you're hovering on the ground. Max landing weight isn't really applicable in the same way to a vertical landing

By conserve you mean collect for later use I am assuming. While it is technically feasible to do that it is extremely impractical. You'd have to either have another aircraft fly in formation in some sort of reverse in-air refueling system, or the pilots would need to fly over a system on the ground which would collect the fuel.
Any system to do this would require precision on the part of the aircraft needing to dump fuel, and in the kind of emergency where dumping fuel is required precision is one thing you aren't likely to get. Also, the cost of implementing a collection system far outweighs the cost of the fuel you'd save.

The dumped fuel does not usually reach the ground but instead evaporates in the air. It eventually will reach the ground, but extremely diluted as part of rain.

@JanHudec We should just train crews for an engine-out low pass so they can collect it off the runway.

@fooot: Whow, that wing is low.

I suppose the least expensive way to do it would be to reinforce the airplane structure so that it coud land at maximum takeoff weight. Then no dumping would ever need to occur.
Still not cheap enough to be practical, though. The weight of that extra structure would take fuel to carry around at all times, to save fuel only on the rare emergency.

Not all planes have the option of dumping fuel, but they just accept overweight landing and the possibility of inspections.

The pilot can either keep circling around to burn it off (doesn't conserve it) or just land overweight without jettisoning.
Burning it off is not an option if you want to get on the ground now to deal with the emergency. And landing overweight can create a new emergency if the gear collapses/too many tires blow.

Is there any way that we can develop a system that can conserve the fuel being dumped.

@prakash What do you mean by "conserve"?

We know that plenty of fuel being wasted during fuel jettisoning. Why don't we develop a mechanism or a system that helps to collect the fuel being dumped from the aeroplane...

@prakash Relative to total fuel used, there is very little fuel dumped. I'm sure that the amount of fuel dumped is far smaller than the additional fuel you would burn if you carried around the extra weight of whatever you could come up with to prevent the waste of dumping. In 12 years of flying aircraft that could dump fuel, I only had to dump fuel once.


text:
What safety requirements are there when designing an electronic device to go inside the cabin of an airliner?
I am considering designing and building an automatic air-sampling unit that can be placed in the cabin of an airliner and left unattended for an extended period of time.  The device will use an electronic air sensor and (small) processor so that it can detect and sample fume events without crew intervention, will be battery powered using a small battery of a known-reliable type (i.e. not Lithium-Ion :), will not have any functions that intentionally emit RF, and will be packaged in an enclosure (either plastic with internal shielding or metal).
What EMC and electrical-safety requirements/specifications must this device meet in order to avoid posing a hazard to the aircraft it is placed on, and how do I ensure that this box is not mistakenly considered a security threat to the aircraft?

I am assuming from your description this is not a permanent part of the aircraft and is just an instrument that will be brought on board. The DO-254's cited by Porcupine above are authorized under FAR 25.1309 which is only for permanent equipment that are an integral part of the aircraft design, not cargo items.
In general, there are no FAA regulations about that kind of equipment, other than hazardous cargo materials (flammables, lithium batteries, etc). Even radios and RF emitters are ok, if the airline company and pilot agree to it. Flight crews sometimes bring their own personal radios on board as backups, for example.
The policy about bringing something like this aboard would largely depend on the owner/operator and one might have completely different requirements or reaction than another. Your best bet would be to contact the operator (airline company) you want to work with and ask them what their requirements are.

It is indeed an instrument that would be brought on board, although the RTCA specs do seem like a good idea anyway.

A document called RTCA DO-160 defines the testing for a number of environmental requirements. Within each test standard is normally a number of different test conditions. The level of required testing is normally defined by the customer of the device, who has the task of showing the regulating body (FAA, EASA, etc) that this is sufficient to ensure the aircraft meets all regulatory requirements.
In addition, DO-254 gives guidance for electronic hardware and DO-178 handles software. There are other legacy documents like MIL-specs that define testing as well.

While this addresses environmental (EMC, electrical safety, ruggedness) quite well, this doesn't touch on the security side, which is just as much a concern in today's paranoid world...

Others will have to pipe in on the security issue, but I suppose if this device is installed in the aircraft like any other installed component then there shouldn't be much of a concern. The installation of the device would have to be disseminated to each crew.

@UnrecognizedFallingObject the security side will require you working with the airline you are going to place these devices on.


text:
How to do a Rapid Descent in a jet with inoperative spoilers?
So, let us assume you are in a simulator for your favorite jet plane, and the instructor gives you a LOFT (Line-Oriented Flight Training) scenario that goes as follows:

A normal takeoff and climb to cruise altitude, and perhaps thirty minutes of normal cruise flight
The non-recoverable loss of speedbrake (flight spoiler) functionality due to a mechanical jam, or some other malfunction such as the loss of all SECs in a FBW Airbus.
Another 30 minutes of time to deal with the first malfunction: run the checklists, plan and initiate a diversion if needed.
You lose normal cabin pressure for some reason, and have to conduct a rapid descent to get back to 10,000' and complete your diversion.

How do you execute the descent, considering that the rapid descent procedures for most jets rely on using the speedbrakes to achieve a high descent rate without overspeeding the aircraft?  To use the 737 QRH checklist for Emergency Descent as an example:

EMERGENCY DESCENT . . . . . . . . . . . . . . . . . . . . . .Announce
The captain will advise the cabin crew, on the PA system,
  of impending rapid descent. The first officer will advise
  ATC and obtain the area altimeter setting.
ENGINE START switches . . . . . . . . . . . . . . . . . . . . . . . . CONT
THRUST levers . . . . . . . . . . . . . . . . . . . . . . . . . . . . CLOSE
Reduce thrust to minimum or as needed for anti-ice.
SPEED BRAKE . . . . . . . . . . . . . . . . . . . . . . . . . FLIGHT DETENT
DESCENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Initiate
Target speed . . . . . . . . . . . . . . . . . . . . . . . . . . . Mmo/Vmo
If structural integrity is in doubt, limit speed as much as
  possible and avoid high maneuvering loads.
Level-off altitude . . . . . . . . . . . . . . . . . . . Lowest safe altitude
                                            or 10,000 feet, whichever is higher

Whenever I see a question title like this, I imagine some pilot somewhere hurriedly typing out his question hoping for an answer before he hits the ground...

The answer is actually quite simple.
FOLLOW THE MANUFACTURES PROCEDURES.
In some aircraft (I don't have a 737 flight manual handy) there is an altitude limitation if the spoilers are inop for just this scenario.  When the aircraft was certified, they needed to demonstrate an emergency descent (in the allowable time) without them, and that might not be possible from the certified ceiling. If that's the case in the 737, then descend to the max altitude with spoilers inop (assuming that you started above it).
If there is no altitude limitation and no special spoiler-inoperative emergency descent procedure (I have never seen one of those, but there's nothing to say that a manufacturer couldn't have one) then you simply fly the regular procedure without spoilers.  The manufacturer had to demonstrate this during certification and it must have been acceptable at the time.
As rbp says, most of the time you fly Mmo/Vmo at idle power after you don the oxygen mask.  IF the flight manual/checklist says that you can put the gear down (some do) then you may, but I wouldn't otherwise.  I certainly wouldn't slow to gear speed (unless the manufacturer says to....  Unlikely in a jet like this) because you are decreasing the drag by slowing, and taking time at altitude to do so.

good answer. cruise in the flight-levels in my aircraft (M20M) is near or below Vlo (140), so I can put the gear down immediately. Vle is 165, so that's the airspeed of an emergency descent, with gear down and the speedbrakes out (which have no operating limitations). gets about 4000fpm descent, which is 4 minutes from the service ceiling of 25,000ft down to 10,000.

@rbp Is that what the manufacturer procedure says to do for your airplane?

yes, and that's what I practiced at the Flight Safety Mooney course in San Antonio. I got a high-altitude endorsement in a 737 level D at Continental

Go to the top right corner of the envelope and stay there (point D in the sample below. Sorry, I don't have the 737 envelope at hand). Engines idle, speed and load factor as high as allowed.

If airframe integrity is not critical, lower the gear to increase drag, but expect to lose the gear doors.

Can you post a larger version of that figure, or point me at where I can find one?

@UnrecognizedFallingObject: I took it from the Wikipedia page for "flight envelope". Try this - I will replace the picture in my answer with it.

So, starting from cruise flight, you'd pull the engines back to idle, then pitch up past alpha-crit to initiate the descent? In other words, you'd be stalling at high IAS to emulate the airflow separation and resulting sink you'd otherwise get from the deployed spoilers?

@UnrecognizedFallingObject: Not at all! Yes, power to idle, but then nose down and a steep turn, so the load factor goes up. Nose down as much as needed to stay at maximum speed.

So, basically, a split-S-like then!  Thanks!

@UnrecognizedFallingObject: Not like a split-S at all! Spiralling descent with down pitch at most 15-20° while keeping tightest turn allowed (60-70° bank, 2-2.5G load for typical airliner).

@UnrecognizedFallingObject More like a steep spiral. A split-S is a roll to inverted and half loop to end up right side up with a 180 deg course reversal. You wont find that in any transport category abnormal procedures.

Ah, thanks for straightening me out then, pardon the pun.  I'm not sure why my brain didn't get to a spiral descent straight away from your description!

This is the correct answer for a non-transsonic aircraft. In  transsonic aircraft, like a 737, the max allowable airspeed is not constrained by Vne, but by Vmo

And unlike Va, Vne is not calculated based on structural considerations but aerodynamic ones.

I would strongly recommend following the manufacturers recommended procedure (which was probably determined using this or a similar method, along with other considerations) rather than creating your own....

Whenever trying to rapidly descend, you always want to think drag!
Throttle to idle, lots of s-turns, (aileron drag), get down to gear speed, drop the gear, and lower flaps if practical.
A limited crabbing-like manuever (intentional side-slipping) would greatly slow the aircraft as well!
I'm sure that Terry will be here to recant us with a tale soon!

Although I am hesitant to say flaps, because they increase lift.

+1 for mentioning sideslipping and Terry. I am waiting myself ...

NEVER SKID AN AIRPLANE, it will cause it to flip over.
what you want to do is a sideslip, not a skid

@rbp It won't flip, (unless you done goof), but you are correct, a sideslip is more accurate.

"unless you done goof"? what does that mean? Next time you're in the air, initiate a 30 degree turn, keep feeding in the rudder on the downward wing side of the aircraft. Make sure you've got a parachute on, and are in an aircraft certified for aerobatics and are at an appropriate altitude. I'll post my unusual attitude training video later today.

here's me in a skidding demo: https://www.youtube.com/watch?v=juu7JoSDE1A

There primary consideration in an emergency descent is to descend at the maximum allowable airspeed in the given configuration.
In a jet, this is based on the "barber pole" on the airspeed indicator (which changes based on altitude).
If the speedbrakes fail, you won't get the maximum descent rate, but you won't break the airplane by flying outside the aerodynamic envelope, either.
Here's a jet-type airspeed indicator with a red and white barber pole: http://www.md80.it/cockpit/cockpit/captain/kuvat/asi.jpg
(I have a high-altitude endorsements as per 61.31(g))


text:
Can a bullet hit make the cockpit door open?
If there is a hijack situation and the terrorist guy shoots at the cockpit door to go inside, will that work?
Are the cockpit door locks in commercial planes like 737s etc good enough to handle a bullet shot?

people often erroneously focus on a door's lock, it's often easier to look for other weak points than going for the lock. I don't know the quality of cockpit doors, but I assume it's the same here.

I feel it is not appropriate to discuss such security sensitive information in public. Related meta discussion.

I agree with DektaLima, this is too sensitive to be discussed.

It's widely that the doors themselves are bulletproof; it seems likely that the locks are, too

@PeterKämpf woah! Nobody in the linked discussion seemed to suggest closing such questions. I can totally understand that many people here can't talk about this, to the degree that it may even be unanswerable, but in no way is it off-topic. Also I'm not convinced this isn't answerable for non-US matters.

I vote this can be answered. Either by quoting regulation saying it is required or lack thereof. Any regulation is publicly available,right? Im working on it.

my main focus for the question was if their are any weak points which are known w.r.t to cockpit doors.  know it might be security concern but i guess there should be some regulations related to it and if not they can be made. I know the sensitivity of this but i don;t feel enough justification is there to put it on hold or marking it UN-answerable...

@vasin1987 At least in the case of the U.S., no. It's not at all uncommon for security-related regulations to be non-public information here. It's very common for them to be some form of controlled unclassified information and not unheard of for them to be classified. (Yes, I've had to deal with the latter... it's really fun when they decide to tell you can't export something, then they won't tell you why or what you could change to make it exportable.)

It's not sensitive security information because of the scope of the question.  If you applied a bazooka to an airplane door, the door would lose, and that shouldn't surprise anyone.  The real reason this question needs to be closed is because the scope is far too broad.

The FAA standards seem to anticipate the use of firearms by people attempting to gain unlawful access to the cockpit.
Opening locks with firearms is probably not as successful as TV would have you believe.

Cockpit Door Standards

Press Release – FAA Sets New Standards for Cockpit Doors
  Release No. APA 01-02
  January 11, 2002
  Contact: Alison Duquette  Phone: 202-267-3462 WASHINGTON, DC
  In response to President Bush's call to strengthen aircraft security, the
  U.S. Department of Transportation's Federal Aviation Administration
  (FAA) today published new standards to protect cockpits from intrusion
  and small arms fire or fragmentation devices, such as grenades. The
  Aviation and Transportation Security Act authorizes the FAA to issue
  today's final rule that requires operators of more than 6,000
  airplanes to install reinforced doors by April 9, 2003.

From FAA Press Release
This press release doesn't actually say that the locks on the doors must resist being fired on using handguns but it is apparent that the scenarios envisaged included those where handguns were present. There are obviously other measures to prevent passengers carrying combat shotguns into the cabin surreptitiously.

Guns and Locks

In movies and television, a locked door, or a padlock on a cage is never an impediment so long as the Hero has bullets to spare. One or two shots is generally enough to destroy the lock, allowing the door to open.
  Unfortunately, in real life — as shown by the MythBusters — this requires a high powered gun at close range, which causes lots of very dangerous shrapnel. Lesser firearms, especially handguns may harmlessly bury rounds in even standard padlocks to little effect. Only SWAT teams and soldiers ever do this in real life, and it involves a shotgun, Kevlar body armor, specialized ammunition (a powdered metal breaching round, often jokingly referred to as "Avon Calling"), and full face protection. Even then, the goal is not specifically to destroy the lock, but to destroy the surrounding door or the hinges.

From TvTropes Shoot out the lock

Other references

Mythbusters - shooting locks


text:
Is there a ceiling on weather patterns?
I know there are winds and other effects at very high altitudes but how high can storms with lightning and rain be?
Bottom line, let's say you are flying a craft with the ceiling of a U-2, can't you fly over any storm?

I believe that the X-15 could fly high enough to not worry about weather (considering that it actually reached space).

@cpast, I'm asking about the weather not which craft(s) can outfly it.

@cpast: There are weather effects in space

Severe convection will have anvil tops at the tropopause and overshooting tops can penetrate much higher (severe thunderstorm warnings often use a value of 60,000 ft for threats to aircraft).  How high the overshooting tops can get is a balance of the positive buoyancy during parcel ascent against the negative buoyancy once it gets into the warming stratospheric air.
A U2 could overfly these storms, but most aircraft are not designed for stratospheric flight (due to the temperature increasing with height in the stratosphere) and any commercial aircraft will be unable to go over these storms.

Why do you say the temperature increases with height? Doesn't it get colder when you go higher? Or are you talking about something like friction with the outside air?

@midnightBlue in the stratosphere temperature increases with height due to absorption of shortwave radiation by ozone.

Ok! So basically there is less absorption of the radiation the higher you go?

@midnightBlue See http://www.srh.noaa.gov/jetstream/atmos/atmprofile.htm

No.  Sprites, also known as upper atmosphere lightning, occur from 31 to 56 miles AGL. (source: Wikipedia) So weather phenomena routinely exceed your U2's altitude by a lot!
Now are Sprites dangerous to flight?  Unknown. I know of no case where an aircraft has been hit by a Sprite.

31 miles is well above even the U2's flight ceiling, so while it's not true that you could always go up to escape weather, Sprites aren't really an issue. I hope that made sense.

Nifty, so these Sprites are the only weather phenomena that could potentially hurt me? Also, the wiki article does cite this as a possible incident involving a balloon...

Aren't aircraft (at least large metal skinned aircraft) generally immune to lightning? Would a sprite strike be any different than a 'normal' lightning strike (which relatively common)?

@Johnny Yep, the Faraday Cage.  Lightning may cause damage to the surface it touches, especially in composite materials, but electronics are protected and a strike isn't going to bring down an aircraft.

@SHAF unless the EM fluctuation fries them


text:
Which kind of identification and authentication is used to secure an airplane?
What does the pilot use? a password? my wife identifies and authenticates herself to her car every morning using her car keys. I don't see the pilot in movies use a similar key?! I don't expect the designers to leave an airplane open for any attacker to go to the cabinet and fly away.

Most small planes do have keys, just like car keys.  For commercial jets, how much time do they spend parked where someone could steal them?  Seems like most are in constant service or in maintenance.  And if you steal one while it's in service... Well, that's hijacking, isn't it?

Most smaller propeller planes have nothing. When you're in you can fly away. This seems to be the same for those private jets and older Boeings. I don't fly planes, but I've seen that Airplane Repo program on Discovery, and they just get in and fly away. How this works with the newest planes - no idea.

So we secure a car but not a jet?

The bigger the plane, the more likely that it's parked at a big airport. Big airports have access controls to the tarmac, enforced with armed guards. They also have mandatory ATC clearance before taking off, and bigger planes are very likely to have a flight plan (it's not always required, but it's odd to not have it and can get a call to the airline). Basically, it's really hard to pull off stealing a big plane.

Not to mention you don't start a jet by just flipping a lever

Also what are you going to do with the stolen plane? Every plane has a tail number and is registered and if a plane misses an inspection it loses its airworthiness certificate and makes it illegal to fly. And no self respecting pilot will buy a used plane without the proper paper trail unlike with a car.

@ratchetfreak Strictly speaking, you could paint over a tail number with a fake one (not an officially assigned one, just paint something on the tail over top of the old number). Still makes it very difficult to flip it because you don't have the paperwork, which is why the best way to take a plane without the previous owner's permission is to have a court order awarding you the title (but that's no longer stealing it).

For smaller aircraft there often isn't anything, but some (especially newer models) do have an ignition much like a car
Some small aircraft and many business jets have an entry key - ie for the doors. It's hard to start the engine if you can't get on board the aircraft! This is especially common for aircraft which are parked at insecure airports.
Commercial airliners usually have nothing, but they are also very difficult to get to, never mind start. If you manage to get to one, sit there for long enough to start it, taxi it to a runway and takeoff..., you'd have taken long enough to alert the authorities and immediately get shot down

Still it sounds strange that an industry with such high security standards leaves an elementary security hole. Of course the chances of anybody actually trying to steal an airliner are very slim, but the same is true of anybody actually trying to hijack or blow up one. Btw assigning a password to the PIC as part of the usual assignment procedure would not be so impractical. Then the valid passwords should be changed for ervery flight of course, which is very possible using smart software.

The security is abstracted from the aircraft: it shouldn't even be possible to get close to one. Answer this: when was the last time one was stolen?


text:
Do you need FAA approval to land a helicopter on Miami Beach?
Do you need FAA approval to land a helicopter on Miami Beach, Florida?

To narrow this down, do you mean the actual beach front, within the city of Miami Beach? or do you mean anywhere in the city?

No; you may need permission from the local authority.  FAA doesn't regulate where you can land or take off.

Unless that place happens to be a controlled field!

If you are in an emergency then get on the ground and deal with the fallout after everyone is safe and sound.
Besides that it's the land owner's call about whether you can land on his property, otherwise you will be trespassing with all due consequences.